<<BACK TO PREVIOUS

Navigator finds out where it is

One of the problems when you don't know where you are is that your GPS satellite navigation system doesn't know either. Now California-based communications technology company SiRF Technology Holdings claims to have come up with an answer.

It says its SiRFInstantFix will allow navigation devices to get their first fix on positioning as quickly as eight seconds “even through urban canyons, dense foliage and in other weak-signal situations”.

The device eliminates the initial time-consuming task of obtaining precise GPS satellite location data – ephemerides – from the satellites themselves. Instead, it uses a set of algorithms to predict seven days of ephemerides and distills them down to a small file that can be used to pinpoint every GPS satellite. This means they can start tracking satellites faster and accept even weak or interrupted signals.

The difficulty that the system overcomes is the need for the GPS receiver to know precisely where each GPS satellite is before it can get a fix.

Since each satellite broadcasts its location every 30 second, if anything interrupts the broadcast, the receiver has to wait another 30 seconds to get another fix. In built-up areas where line of sight is interrupted, it can take several minutes to get all the information.

With the SiRF system, the user does a weekly synchronisation of where the satellites are and downloads a small file that enables a fix to be obtained from even sketchy parts of a satellite signal in most cases.